The day begins with the march of the downsizers — those “consultants” hired by big businesses to come in and do the dirty work of laying people off. Maybe one of the guys they cut (Stanley Tucci) is in charge of “risk management,” and maybe he’s been working on something. If he’s a loyal soldier, and somebody dependent on his severance check clearing, he alerts an underling (Zachary Quinto).

And that young guy does the math. They’re “exposed,” in a big way. And “once this gets going in the wrong direction,” their 107 year old firm, Wall Street and the world’s economy will tumble off a cliff. How that firm, its leaders and its foot soldiers react to this nightmare scenario is the subject of the superb Wall Street thriller “Margin Call.” Over the course of hours, fateful decisions will be made, employees will face moral and ethical choices and all of it will have to happen in utmost secrecy.

“These people,” Quinto’s math whiz Seth mutters and the outside world, “walking around with absolutely no idea of what’s about to happen.”

“Margin Call” isn’t a sermon, it’s a dissection, an all-star big-name top-to-bottom/bottom-to-top analysis of the sorts of people and the kind of mindsets that brought the world to its dire financial state today. The casting is spot on. Paul Bettany is the free-spending role model of what employees at this place aspire to be — greedy, self-interested, driving an Aston Martin. Kevin Spacey is the seemingly heartless boss whose callousness masks inner pain.

“Now they’re gone,” he says of the laid off. “They’re not to be thought of again.”

But they’ve got to find the man who was onto this (Tucci). And he can’t or won’t be found. Midnight meetings hurl layers of management (Demi Moore and Simon Baker, and eventually Jeremy Irons) at a problem they don’t quite understand. That’s one of the great lessons of writer-director J.C. Chandor’s debut feature film. There are smart people on Wall Street. But they’re as rare there as anyplace else.

“Be first. Be smarter. Or cheat,” is the motto of their fearless leader (Irons).

This compelling-acted film explains, better than any soundbite, why people have taken to the streets, “occupying” centers of finance. If their rage is unfocused, “Margin Call” suggests, that’s with good reason. There are no real heroes or villains here, just human beings with human failings making BIG human mistakes.